1. Field of the Invention
The present invention relates to a circulation system for a high refractive index liquid, used for circulating the high refractive index liquid in a pattern forming apparatus that includes a resist coating/developing section and an immersion light exposure section. The resist coating/developing section is structured to perform resist coating on a substrate, such as a semiconductor substrate, and development after light exposure. The immersion light exposure section is structured to subject a resist film formed on the substrate to light exposure in accordance with a predetermined pattern while immersing the resist film in the high refractive index liquid. The present invention further relates to a pattern forming apparatus and pattern forming method using a circulation system for a high refractive index liquid.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, photolithography techniques are used for forming circuit patterns on semiconductor wafers. Where a circuit pattern is formed by use of photolithography, the process steps are performed, as follows. Specifically, a resist liquid is first applied to a semiconductor wafer to form a resist film. Then, the resist film is irradiated with light to perform light exposure on the resist film in accordance with the circuit pattern. Then, the resist film is subjected to a developing process.
In recent years, the integration degree of semiconductor devices becomes increasingly higher to improve the operation speed and so forth. Accordingly, photolithography techniques are required to increase the miniaturization level of circuit patterns formed on semiconductor wafers. As a photolithography technique for realizing a high resolution of a 45-nm node level, there has been proposed the following immersion light exposure (for example, see U.S. Patent Application Publication No. US 2006/0231206 A1). In this immersion light exposure, a light exposure liquid, such as purified water, having a refractive index higher than air is supplied between the semiconductor wafer and light exposure projection lens. The wavelength of light radiated from the projection lens is shortened by means of the refractive index of the light exposure liquid, so that the line width obtained by the light exposure is decreased. Further, in order to attain a higher resolution, there has been proposed a technique for performing immersion light exposure while using a high refractive index liquid as a light exposure liquid (see “Development of new high refractive index liquid (Delphi) for next-generation immersion light exposure in semiconductor manufacturing,—realizing micro-fabrication of 32 nano-meter line width—,” Sep. 12, 2005, Mitsui Chemicals, Inc. (authorship unknown); Internet [mitsui-chem.co.jp/whats/2005—0912.htm]). According to this technique, the high refractive index liquid is formed of a liquid compound comprising a cyclic hydrocarbon skeleton and having a higher refractive index than purified water, with which a high resolution of a 32-nm node level is realized.
In general, cleaning (or rinsing) of a semiconductor wafer is performed by use of a cleaning liquid (or rinsing liquid), such as purified water, before and after immersion light exposure (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2006-80403). Cleaning performed before immersion light exposure is conceived to improve the affinity relative to the light exposure liquid. Cleaning performed after immersion light exposure is conceived to remove part of the light exposure liquid left on the semiconductor wafer.
However, where a high refractive index liquid is used as a light exposure liquid, as described above, the conventional cleaning may bring about following problems. Specifically, in the case of cleaning performed before immersion light exposure, the cleaning liquid and light exposure liquid come to be greatly different in physicality, so the resist film suffers bubbles and liquid residues generated during the immersion light exposure due to the residual part of the cleaning liquid. Further, since high refractive index liquids have a high viscosity, it may be difficult to satisfactorily remove the light exposure liquid by cleaning performed after the immersion light exposure. Accordingly, where a high refractive index liquid is used as a light exposure liquid, the conventional cleaning may deteriorate the process uniformity, when performed before and after the immersion light exposure.
On the other hand, in light of the cost and environment, the consumption of the light exposure liquid and cleaning liquid should be smaller. Particularly, since high refractive index liquids are expensive in general, a process performed by use of a high refractive index liquid is strongly required to decrease the consumption thereof. In order to decrease the consumption of the light exposure liquid and cleaning liquid, these liquids may be recycled by circulation. However, where the light exposure liquid and cleaning liquid are recycled by circulation, each of these liquids requires a mechanism and treatment for regenerating used liquid, which complicate the entire apparatus and process.